Diodes ZXBM5210 - Manual (Page 6)

ZXBM5210
Document number: DS36765 Rev. 1 - 2
6 of 17
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December 2013
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ZXBM5210
Application Note
(cont.)
Motor Speed Control with DC Voltage on V
REF
Pin
Motor speed can be controlled by adjusting the DC voltage into the V
REF
pin. The output drive PWM duty ratio is defined by the ratio of the V
REF
voltage to the supply V
DD
voltage.
In V
REF
speed control mode, FWD and REV pins are only used for direction control and therefore high frequency PWM control signal should not
be applied to the FWD and REV pins. If repetitive direction changes required, it is recommended to keep direction change frequency of below
400Hz.
The speed and direction control is given by:
FWD REV V
REF
OUT1 OUT2 Operating mode
L L x Open Open Standby mode – All switches are off
H L V
DD
H L Forward mode – Current flows from OUT1 to OUT2; 100% duty
H L 3V to V
DD
H L Forward mode – Current flows from OUT1 to OUT2; V
REF
duty control
L H V
DD
L H Reverse mode – Current flows from OUT2 to OUT1; 100% duty
L H 3V to V
DD
L H Reverse mode – Current flows from OUT2 to OUT1; V
REF
duty control
H H x L L Brake mode – Short circuit brake with low side switches on
Motor Speed Control with a PWM Input Signal
Motor speed can be controlled by adjusting the duty cycle of the PWM speed control signal into the FWD or REV while keeping the V
DD
pin at
the nominal motor voltage. In this mode the input voltage on the V
REF
pin must be greater than or equal to V
DD
.
In PWM speed control mode the high side switches S1 and S3 are kept fixed while the low side switches S2 or S4 are switched. In the forward
mode, S1 is kept switched on, S2 is switched in accordance with the PWM signal and S3 and S4 are switched off. In reverse mode, S3 is
switched on, S4 is switched in accordance with the PWM signal and S1 and S2 are switched off.
The speed and direction control is given by:
FWD REV V
REF
OUT1 OUT2 Operating mode
L L x Open Open Standby mode – All switches are off
H L V
DD
H L Forward mode – Current flows from OUT1 to OUT2; 100% duty
L H V
DD
L H Reverse mode – Current flows from OUT2 to OUT1; 100% duty
H H x L L Brake mode – Short circuit brake with low side switches on
PWM L V
DD
H PWM
Forward mode – Current flows from OUT1 to OUT2;
PWM control mode
L PWM V
DD
PWM H
Reverse mode – Current flows from OUT2 to OUT1
PWM control mode
H H x L L Brake mode – Short circuit brake with low side switches on
The motor speed is proportional to the input PWM signal duty. For example, for a 12V motor the V
DD
pin is maintained at 12V while varying the
PWM control signal duty to adjust the motor speed linearly. The timing diagram below shows the output O1 and O2 in relation to PWM speed
control signal at PWM pin.
Frequency of PWM speed control signal can be between 8kHz to 100kHz. Recommended typical PWM signal frequency is 25kHz to keep
switching frequency away from the audible band.